怎么用java实现排序

Question

已知A、B、C、D、E，其中B的子集为A，C的子集为AB，D的子集为C，E的子集为B。要求按照大小排序，如果没有子集，则默认值为0，有则按照最大的子集+1进行排序。

Answer 1

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

class Element {
    public String name;
    public String subset;

    public Element(String name, String subset) {
        this.name = name;
        this.subset = subset;
    }
}

public class SubsetSort {
    public static void main(String[] args) {
        List<Element> elements = new ArrayList<>();
        elements.add(new Element("A", ""));
        elements.add(new Element("B", "A"));
        elements.add(new Element("C", "AB"));
        elements.add(new Element("D", "C"));
        elements.add(new Element("E", "B"));

        Collections.sort(elements, new Comparator<Element>() {
            @Override
            public int compare(Element e1, Element e2) {
                if (e1.subset.isEmpty() && e2.subset.isEmpty()) {
                    return 0;
                } else if (e1.subset.isEmpty()) {
                    return -1;
                } else if (e2.subset.isEmpty()) {
                    return 1;
                } else {
                    return Integer.compare(e2.subset.length(), e1.subset.length());
                }
            }
        });

        for (Element e : elements) {
            System.out.println(e.name);
        }
    }
}